Who I have the same questioned this topic

In order to save data, I have 3G turned off and wireless turned on.  Of course, I don't always have a wireless connection, so if I receive a voicemail, visual voicemail doesn't work.  As a result, I call my voicemail to retrieve the message.

How can I add my voicemail password to the voicemail number?

I would love to do what I did with my previous phone: *86 (or whatever) pp <password>.

Is that possible on iPhone 4s?